The importance of molecular dating analyses for inferring Hawaiian biogeographical history: a case study with bark lice (Psocidae: Ptycta)
The use of intuitive or explicit biogeographical reconstruction techniques to estimate the timing of species radiations on the Hawaiian Islands, while often incorporating evidence on the timing of island formation, may be misleading if the effects of extinction are overlooked. Using phylogenies of the bark louse genus Ptycta (Psocidae), we compared results from biogeographical character mapping with those from molecular dating analyses. These results were used to evaluate the ‘progression model’, which predicts an oldest-to-youngest pattern of island colonization.
The main Hawaiian Islands (Kauai, Oahu, Maui, Lanai, Molokai and Hawaii).
With a data set including 101 Hawaiian Ptycta specimens and 18 outgroup species, we constructed molecular phylogenies based on sequences of the nuclear gene wingless and mitochondrial genes 12S, 16S and cytochrome c oxidase subunit I (COI). Maximum-likelihood, maximum-parsimony and Bayesian phylogenetic analyses were used. We used beast to estimate a time-calibrated tree under a relaxed clock model.
Our analyses suggested a single colonization event, followed by extensive movement of Ptycta among islands and species radiations within and between islands. This monophyletic radiation is composed of two well-supported clades that are also supported by two synapomorphic characters of the male genitalia.
Very different biogeographical patterns are inferred by molecular dating versus approaches based on character mapping. Simple biogeographical reconstruction over the molecular phylogeny supports a pattern of youngest-to-oldest island colonization, the reverse of that predicted by the ‘progression model’, and implies that this radiation could be as young as the most recent islands of Maui (1.4 Ma) or Hawaii (0.5 Ma). Molecular dating, however, infers a pattern consistent with oldest-to-youngest island colonization, and suggests a lineage age of 7.1 Ma. Extinction on the oldest island of Kauai may account for the differences in results between the two analyses.